Process for manufacturing polyene esters and acids

Abstract

A process for the manufacture of polyene esters or polyene acids comprises reacting a polyene O,O-dialkylacetal of di(O,O-dialkylacetal) with a vinylketene acetal or analogue thereof in the presence of a Lewis acid, hydrolyzing the reaction mixture depending on the vinylketene acetal used, subsequently cleaving alcohol under strongly basic conditions from the polyene derivative produced at this stage and, where the desired ester or carboxy group is still not present, performing the respective conversion. Certain intermediates in this process form a further aspect of the invention. The final products are primarily carotenoids which can be used appropriately, e.g. as colorants and pigments for foodstuffs, animal products etc.

Claims

1. A process for manufacturing a compound of formula: ##STR25## wherein A is a monovalent conjugated polyene group or a methyl-substituted, monovalent conjugated polyene group,

B is a bivalent conjugated polyene group or a methyl-substituted, bivalent conjugated polyene group,

R.sup.1 and R.sup.2 each independently is hydrogen or methyl, and

R.sup.3 is hydrogen or C.sub.1-6 -alkyl, with the --CH.dbd.CH--C(R.sup.1).dbd.C(R.sup.2)--COOR.sup.3 group(s) in each case being situated in the terminal position(s) of the conjugated chain of group A or B,

which process comprises:

(A) reacting a compound of formula:

A and B are as above, with the --CH(OR.sup.4).sub.2 group(s) being situated in the terminal position(s) of the conjugated chain of group A or B, and

R.sup.4 is C.sub.1-6 -alkyl, with a compound of formula: ##STR26## wherein R.sup.1 and R.sup.2 are as above, and

R.sup.5 is C.sub.1-6 -alkyl and

R.sup.6 is C.sub.1-6 -alkyl or tri(C.sub.1-6 -alkyl)silyl, or R.sup.5 and R.sup.6 both are tri(C.sub.1-6 -alkyl)silyl, or R.sup.5 and R.sup.6 together form 1,2-ethylene or 1,3-trimethylene, in the presence of a Lewis acid, and where a compound of formula III in which R.sup.5 and R.sup.6 both are C.sub.1-6 -alkyl or both are tri(C.sub.1-6 -alkyl)silyl or together form 1,2-ethylene or 1,3-trimethylene is used, subsequently hydrolyzing the compound formed, so as to form in all cases a compound of the formula: ##STR27## wherein A, B, R.sup.1, R.sup.2 and R.sup.4 are as above, with the --CH(OR.sup.4)--CH.sub.2 C(R.sup.1).dbd.C(R.sup.2)COOR.sup.7 group(s) being situated in the terminal position(s) of the conjugated chain of group A or B, and

R.sup.7 is C.sub.1-6 -alkyl, hydrogen, 2-hydroxyethyl or 3-hydroxy-n-propyl;

(B) cleaving off the R.sup.4 OH group from the compound formula IV' or IV" under strong basic conditions; and

(C) where there is a difference between groups --COOR.sup.7 and --COOR.sup.3, converting group --COOR.sup.7 to group --COOR.sup.3.

2. The process according to claim 1, wherein the reacting involves a compound of the formula:

R is a group (a), (b) or (c) ##STR28## in which R.sup.4 is C.sub.1-4 -alkyl,

R.sup.8 and R.sup.9 each independently is hydrogen, a hydroxy group, a protected hydroxy group, an oxo group or a protected oxo group,

m is 0, 1, 2, 3 or 4,

n is 0 or 1,

p is 0, 1 or 2,

q is 0, 1, 2 or 3, and

r is 0, 1 or 2,

3. The process according to claim 2, wherein R is a group (a) and a protecting group is present, the process further comprising cleaving the protecting group.

4. The process according to claim 1, wherein the compound of formula II' or II" is reacted with a compound of formula III in an organic solvent at temperatures in the range of from about -40.degree. C. to about 100.degree. C. in the presence of a Lewis acid selected from the group consisting of zinc chloride, zinc bromide, titanium tetrachloride, lithium perchlorate, boron trifluoride etherate, and iron(III) chloride.

5. The process according to claim 4, wherein the organic solvent is selected from the group consisting of lower aliphatic hydrocarbon, cyclic hydrocarbon, lower, halogenated aliphatic hydrocarbon, lower aliphatic ether, cyclic ether, lower aliphatic nitrile, and aromatic compounds.

6. The process according to claim 5, wherein the organic solvent is selected from the group consisting of n-pentane, n-hexane, cyclohexane, methylene chloride, chloroform, diethyl ether, tert.butyl methyl ether, tetrahydrofuran, acetonitrile and toluene, and the reaction of the compound of formula II' or II" with the compound of formula III is effected in the temperature range of about -20.degree. C. to room temperature.

7. The process according to claim 1, wherein the strong base for the cleavage of the alcohol R.sup.4 OH from the compound of formula IV' or IV" is an alkali metal alcoholate or an alkali metal hydride.

8. The process according to claim 7, wherein the cleavage of the alcohol R.sup.4 OH is carried out in a solvent selected from the group consisting of an alcohol, an aliphatic ether, a cyclic ether, an aliphatic ester, an aromatic, an aliphatic hydrocarbon, a lower halogenated aliphatic hydrocarbon and a mixture of an alcohol with another solvent referred to above.

9. The process according to claim 7, wherein the cleavage of the alcohol R.sup.4 OH is carried out using a sodium alkoxide as the base and the corresponding alkanol as the solvent at temperatures between room temperature and the reflux temperature of the respective reaction mixture.